This invention relates to curing agents for epoxy resins. In one embodiment, the invention relates to epoxy resin systems having lengthened working time for applications in high-performance composites.
Epoxy resins are thermosettable materials which can be used, in combination with a selected curing agent, in high-performance applications such as electrical laminates and structural composites. For such applications, it is necessary to design epoxy/curing agent systems which have a combination of high glass transition temperature, flexural strength and retention of modulus when wet. Such properties have been achieved in epoxy systems containing curing agents such as diaminodiphenylsulfone, .alpha.,.alpha.'-bis(4-aminophenyl)-p-isopropenylbenzene and .alpha.,.alpha.'-bis(3,5-dimethyl-4-aminophenyl)-p-diisopropenylbenzene. The first of these suffers, however, from a deterioration of high-temperature properties under moist conditions. The latter two have good retention of high-temperature properties under moist conditions, but for some applications have unacceptably short "out-time," or time during which the system applied to a prepreg remains tacky at room temperature, to permit convenient use in composites.
It is therefore an object of the invention to provide an epoxy resin system which has good high-temperature properties, good property retention in a moist environment, and relatively long out-time.